由于精度问题,必须要开longlong,其实核心代码很简单

#include <bits/stdc++.h>
using namespace std;
int main() {
    string sa;
    long long a = 0, b;
    cin >> sa >> b;
    for (auto& c : sa) a = (a * 10 + c - '0') % b;
    cout << gcd(a, b);
}